Reducing the Diameter of Freight Vehicle Wheels – The Suitability of Q/D as a Control for Wheel-Rail Contact Stress

High wheel-rail contact stress is related to rail damage mechanisms such as gross plastic flow. Such high contact stresses are often generated by freight vehicles which have comparatively high axleloads. On railways in Great Britain (GB) a limit is placed on the ratio of static wheel load (Q) to wheel diameter (D) as a proxy to control contact stress related damage. However, there is increasing interest in the use of
smaller diameter wheels on freight vehicles, in order to prolong wheelset life (smaller scrap diameter) and increase capacity within the GB’s constrained structure gauge.

GB Railway Group Standards [1] limit Q/D to 0.13 kN/mm. However it is known that a number of freight wagons already operate above this limit, either due to derogations granted against the standard, or as a result of being introduced prior to the standard’s universal application (‘Grandfather Rights’). At least one vehicle type is known to operate with a Q/D ratio of up to 0.165 kN/mm.

This paper presents the results of an investigation into the contact stress state of the GB network. This formed part of a larger study [2] undertaken with a view to allowing a reduction in wheel diameters for freight vehicles. The research was conducted as part of the industry’s R&D programme managed by the Rail Safety and Standards Board (RSSB).